Radio location system



5 Sheets-Sheet l J. E. HAWKINS RADIO LOCATION SYSTEM Sept. 15, 1953 Filed Sept. 8, 1951 INVENTQR. Jam e5 1?. Hawkuas I N TSQ J. E. HAWKINS 2,652,560 RADIO LOCATION SYSTEM 5 Sheets-Sheet 3 Sept. 15, 1953 Filed Sept. 8, 1951 5 Sheets-Sheet 4 Sept. 15, 1953 .1. E. HAWKINS RADIO LOCATION SYSTEM Filed Sept. 8, 1951 Ja I BE Sept. 15, 1953 J. E. HAWKlNS RADIO LOCAT-ION SYSTEM Fi led Sept. 8, 1951 5 Sheets-Sheet 5 Patentecl Sept. 15 1953 UNITE STATE" F 35 Claims. "1

The present inventioni'rel'atesi to radio location and distance determiningsystemsand, although not limited thereto, "relates more particularly to improvementsin radio position finding systems of the hyperbolic, *cont'inuouswaveitype employing phase comparisonji'npairs :of position indication signals radiate'dffrom a pluralityofspaced transmitting points to provide one :or more indications from which 'theipos'ition of a mobile receiving point relative to the,.knowng positions of the transmitting points may ."be determined Without ambiguityfa'ndwithjprecision accuracy. "In systems either-particular type referred to, the continuous wavesjradiatedfrom'each pair of transmittersiproduce' standingwaves in space, the phase relationshipfof'whichjohanges as a function of. changingjposition' betweenth'e two transmitting points. More specifically, the standing waves produced {by each fpair of transmitting units of the 'systemiare characterized by isophase lines "which ;are hyperbolic in contour about-the transmitting'pointsasfoci. 'On a line joining the pair of'transmitters, these iso-phase linesmay be spaced"apartanistance equal to one-half of thewavelengthof awave'having a frequency equal to'themean'oraverage frequency of'the radiated waves; and have diverging spacings at points on eitheriside ofthisline, or in an improved systemhereina'fter referred-to may be spaced apart a distance corresponding to-socalled fphantom frequencies representing the sum or difference of the mean or average frequencies. With-this system arrangement, the position of a receiving pointrelative to a-pair of hyperbolic iso-phase" linesmay -be determined by measuring the :phase I relationship between continuous waves'ra'diated from the pair of transmitters.

Since the point of location of the receiving point along the zone separating the two iso-phase lines is not indicated by such a phase measurement, it is desirable to employ at least three spaced transmitters, different pairs of which function to provide a grid-like'pattern of intersecting hyperbolic lines, inorder to obtain absolute determination of the position of the receiving point. ,Systems of the character described are exceedingly accurate in' so far as the position indications produced at thereceiving point are concerned. For thesystem to function, however, it is necessary to maintain phase'synchronization between the continuous "waves radiated by the spaced transmitters, oralternatively, so to arrange the system'thatgphase shifts between-the radiated waves are compensated during the phase "2 comparing operation. Phase synchronization of the waves radiatedfrom theplurality of transmitters presents ani'exceedingly difiicult problem whichhas beenthesdbject of considerable development work.

To obviate-this problem, Systems of the continuous wave hyperbolic" type have been proposed (see Honore United States Patent No. 2,148,267) in which the phase shift'problem is obviated by heterodyning'the carrier waves of each pair of transmitters at afixed link transmitting point, and modulatingthedifferencefrequency component of the hetero'dynedwaves as a reference signal upon the carrier'output ofthe link transmitter for radiation to the receiving point, where the difference frequency "component is detected and phase compared with adifference frequency signal derived bydirectly'heterodyning the transmitted continuous Waves at the receiving point.

In this manneryphase-shifts between the continuous waves radiated'from-the'two transmitters are-completely compensated so that the measured phase angleis truly representative of the location-of the receiving'point between a pair of iso-phaselines.

While the described arrangement for obviating the phase synchronization problem is entirely satisfactory; itentails the use of tWo carrier channels for'thelink transmitters in addition to the threeor four channels taken up by the three orfoursurvey channels in order to makeup -a complete-system. An improved arrangement for eliminatingthe link transmitters withouteliminating the functions thereof is disclosed and broadly claimed in Hawkins and Finn Patent No; 2,513,31'7,--whereina pair of transmitters arealternately operated aslink transmitters and as position signal transmitters. An-

other problem encounteredin the operation of -10- continuous wave systemsf -is that of eliminating ambiguity from the-phase measurements which provide the-desired position information. Thus, while the two' phase; measurements identify the position of the receivingsstation relative to two 7 they do not indicatewhich pairs of lines the inintersectingpairs of hyperbolic- -iso-phase lines,

dicationsare-related to. This; means that in operating the system- -the geographiclocation of the receiving system-must be known at thestart of'movement of the receiving system relative to the transmitting stations-and, furthermore, that the successive wavelengiths. must be counted as the'receiving station is;moved'relati ve to the gridlike "pattern of hyperbolic lines. It also means: that a mobile craftentering the radiation pat- 3 tern of the transmitters cannot utilize the radiated signals to determine its position without employing auxiliary equipment to determine the approximate position of the craft relative to the signal transmitters.

In a copending application Serial No. 138,235 filed January 12, 1950, entitled Radio Location System and assigned to the same assignee as the present invention, there is disclosed an improved radio location system of the continuous Wave type which is free not only of phase synchronization difficulties but also of ambiguity problems. In the system of the said copending application, position indications are obtained having difierent sensitivities, termed phase sensitivities, in so far as the spacing of the isophase lines is concerned. More specifically, a plurality of low phase sensitivity position indications and a plurality of high phase sensitivity position indications are obtained, the low phase sensitivity indications being effective to locate the range of the high phase sensitivity indications and being characterized by widely spaced phase coincidences and the high phase sensitivity indications being characterized by closely spaced phase coincidences. The high and low phase sensitivity indications are obtained by producing pairs of beat frequency signals in accordance with the principles of the Honore system and then heterodyning these beat frequency signals to produce position indicating and reference signals for phase comparison which have phase sensitivities determined by phantom frequencies corresponding to the sum of or difference between the mean waves from which the pairs of beat frequency signals were derived.

While this latter system completely solves the ambiguity problem a considerable number of transmitters and carrier channels are required and a number of transmitters and carrier channels are required and a number of narrow band pass filters must be employed to separate the various position indicating and reference signals, which adds to the expense and may cause phase shift difficulties unless the band pass filters are carefully selected and balanced. In a copending application entitled Radio Location System Serial No. 241,776, filed August 14, 1951, in the name of the present inventor and assigned to the same assignee, there is disclosed and claimed an improved radio location system of the continuous wave type which is free of phase synchronization difficulties of the character mentioned, in which the above mentioned disadvantages pertaining to ambiguity are entirely obviated, and in which the use of narrow band pass filters is minimized or eliminated.

In one embodiment of the invention disclosed in the latter copending application, narrow band pass filters are entirely eliminated, but a rather large number of different frequency carrier channels are required to provide the necessary position indicating signals and reference signal carriers, and in another embodiment a reduction in the number of frequencies requires the modulation of a plurality of reference signals on common carriers and the utilization of narrow band pass filters at the mobile receiving unit.

In accordance with the present invention a completely non-ambiguous system is obtained which while employing a minimum number of frequencies eliminates the use of narrow band pass filters in the signal circuits, eliminates or minimizes the modulation of more than one reffrequencies of the carrier 1 4 erence signal at a time on any carrier, and sub-'- stantially isolates the phase meters from the signal circuits except during periods when the particular signals to be phase compared are being received at the mobile receivingunit thereby eliminating phase meter drift.

It is therefore an object of the present invention to provide an improved radio location system which is free of phase synchronization and phase shift difficulties and which combines economy of frequencies with precision position determination.

It is another object of the present invention to provide an improved radio location system of the continuous wave type which is free of phase synchronization difficulties, in which certain of the position indications obtained have sensitivities, in so far as the spacing of the iso-phase lines is concerned, which will be referred to hereinafter as phase sensitivity, different from the phase sensitivity normally determined by the frequencies of the radiated waves and in which the number of carrier channels employed is minimized.

It is a further object of the present invention to provide a radio position finding system of the character described in which non-ambiguous position indications are obtained.

It is a still further object of the invention to provide a radio position finding system of the character described in which a plurality of low phase sensitivity position indications and high phase sensitivity position indications are obtained, the low phase sensitivity indications being effective to locate the range of the high phase sensitivity indications and being characterized by widely spaced phase coincidences, and the high phase sensitivity indications being characterized by closely spaced phase coincidences.

Still another object of the invention is to provide a radio position indicating system of the character described wherein such high phase sensitivity and low phase sensitivity position indications are obtained while employing a minimum number of carrier frequencies suitable for efficient long range propagation.

It is likewise an object of the present invention to provide improved transmission systems for use in radio location systems of the above indicated character.

It is also an object of the invention to provide improved receiving equipment for use in radio location systems of the above indicated character.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings in which:

Figs. 1 and 2 when taken together. constitute diagrammatic representation of a three-foci position indicating system embodying the present invention, providing an unambiguous position by means of two sets of indications, each set including high and low phase sensitivity indications, Fig. 1 representing the transmitting end of the system and Fig. 2 representing the mobile receiving equipment;

Fig. 3 is a diagrammatic representation of a suitable normally closed gate circuit which may be employed in the equipment shown in Figs. 1 and 2;

Figs. 4 and 5 when taken together, constitute a diagrammatic representation of another form teases of h eefoci. positi'onindi at i Syst m .emb d ing the present invention, Fig, 4 representing the 'transmitting of t e s emand Fi -.5 r s n i the mobi e ee n fi i r pmeili fin c.

i 6 is a a ra t e r s tati n 9f? sui ab ma y ori nta e circuit. ich, m y be employed in the receiving equipment shown in Fi s -In he aw nssisol d n andhro eu in e rows have been employed to indicate the receivi s p i t f nal c a ce and, h so 9 the accepted signals during alternate periods in which certain of the transmitters are alternately operative in accordance with the arrangement d s l d the'e e a d tat et Ne. 2 7 ,3 and as will be more fully described hereinafter.

Referring now to Figs. 1 and? ofthe drawings,

the invention is illustrafid ts lnbodid in a threefoci hyperb lic Continuous wave'systemror providing position information at. a mobile receiving unit it (Fig. 2) which maybe carried by a vesselor vehicle operating vvithinthe radius of transmission of a pluralityof -spaced transmitting units IE 1 and 12. These units are preferably spaced apart approximately equal distances and areso positione'd that the line joining the points of location of'tl'ie units l and I! is angularly related to the line joining the'points of location of the units l i and I2. As is described more fully hereinafter, the transmitting units l0 and I2 are equipped continuously to radiate a pair of position indicating signals in the form of carrier waves of different frequencies and to intermittently or alternately radiate a second pair of carrier waves of still difierent frequencies. On

the other hand, the transmitting unit ll is equipped to continuously radiatea carrier wave of another frequency and alternately to radiate an additional pair of position indicating signals in the form of carrier waves of still different frequencies.

Specifically, the transmitting unit It comprises a continuously operative transmitter'ld and a transmitter which is adapted to' be alternately rendered operative and inoperative by a suitable relay lta. The transmitter '|5 is adapted to radiate a continuous carrier yvave at a frequency of 1752.420 kilocycles and the transmitter l4 consists of a carrier wave oscillator l6 adapted for operation at a frequency of 1700.330 kilocycles,

'a modulator l'l'and a power amplifier H! where- 'by the output of the transmitter l4 constitutes a continuous carrier wave, which, as is more fully described hereinafter, may have suitable modulation signals modulated thereonduring certain :periods of the transmitter operation. Similarly,

the transmitting unit l2 comprises a continuously operative transmitter'lQ' and a transmitter 28 which is adapted tobe alternately rendered 0p- Jerative and inoperative by a'suitable relay'2I.

The transmitter 270 when rendered operative by the relay, radiatesfa continuous carrier wave at a frequency of 17521420 kilocycles and the transmitter l9 includes 'a carrierjwave oscillator"22 adapted for operation at a frequency of 1798.510 kilocycles, a modulatorizt anda pjovver'amplifier 24 whereby the outputofthe transmitter I9 conj stitutes a continuous: carrier Waveiwhich, as is more fully described her'eiiiaftenmay-haVe suitable modulation signals modulatedthereon during certain periods of operation.

The transmitting unit ll includes a continu- 1752.00 kilocycles and apair' of additional 'transmitters 26 and 27 for respectively radiating addi sents slightly less than half 6 tiorial cariierjwaves' areaa cie "f'1'70010bkilocycles' and 1798.00'k'il0dyrile's toge er with's'witching means for'altrnately rendering one or the other of the transmitters 25am 2! operative. In the arrangement illustrated/operation of either or the two tran mipters'zetr 21 'is accomplished by alternately fedingfanode current to the electron discharge tubes of 'the "respj emve transm tters from the positive terminal 2 8 of a suitable anode current 'sourcejnot'shown,'through'acommutating ring 29 which is shaft connected by means of a shaft'3'fl 'so asto'beidrivenata cens'tant Speed by 'a "synchronous "motor and gear faceof the ring, it will be iinderstood thata short off-period signal 'is proyided b'etwensuccessive periods during'vvhich the'transmittersfzfi and 27 are alternately operative "thus preventing simultaneous radiation of *vyave's by both transtransmitters are mer 1y" 'pleratedis; brcourse, dependent upon thespe' 'rlotatio'n of {the mitte'rs. The periodicityjwith which the two 'commutating ring, anainthe articular-embodiment ofthe invention shown, 'the'rirfigf29 is"prf- 40 jerably driven at a speed often revolutions *per second so that the transmitt'ersifi and-21 arealternately rendered :operativeat intervals of one twentieth of a second. v

Referring again to tlietra'ris'mitti'ngunit" [0, this unit comprises, ii -addition to the transmitters M e v I 'cjeivis 3'2 -'and' 33, a frequenc responsive gate means fii; a rectifier and control tube'u'nit' 35 for controlling the relay IS, a mixeror-heterodyning means 36, a low pass filter 3'! and a cyclicallyoprable switch means 38. The gate meanest, in' addition to a suitable gate circuit 3'4awhich wilfbedescribed more fully hereinafter-finconnection With-"Fig.3, includes a 5'1Q'c'yele Eband'passfiltert ib. The

switch meansf s com rise a corninutating "ring made up of a" pair of onducting segments 3 8a and 38b which' ar'e separated-by insulating segments; 38c 'and"- adaptedf'to 'be-"svv'ept' over by" a rotating contact fbrii'sh' 38d, which as ri'iiire "fully explained hereinaftenf is drive at a constant speed and functions alte nately tosupplyfrference signals of requencyto'fthe input terminals of the 'gatecircuit 'Alliofithe' above described equipment which-goes toimalze up the transmitting unit 1 I 0 is connected" as shown in Fig. 1 of the drawing, as *Will becomeclearly-apparent in the description of the" operation.

Thef transmitting nnit "'"l 2 which "is 'subst'antially identical With" the transmitting unit It except for the frequenciesat which variouspieces transmitters l9 and 20, a-pair of fixed tuned of equipment operate, includes; in addition to the receivers-39 and aura "frequency responsivq ate means-4 I a rectifier and control tube unit'flz, a

mixer or-heterodyning means 43; alow= pass filter 44 and a cyclically operable switch means 45 7 which is identical with the switch means 38 at the transmitting unit [0. The gate means 4| includes, in addition to a suitable gate circuit 4la, a 330 cycle band pass filter 41b.

Referring now to Fig. 2, the mobile receiving unit i3 is shown as comprising a plurality of fixed tuned receivers 46, 47, and. 48, of which the receivers 46 and 48 are of the amplitude modulation type, a pair of mixers or heterodyning means 49 and 50, a pair of low pass filters and 52, and a plurality of phase measuring means or phase meters 53, 54, 55 and 56. Associated with each of the phase meters 53 to 56 are a plurality of normally closed frequency responsive gate means each of which includes a suitable sharply tuned narrow band pass filter and a plurality of gate circuits. Specifically, the gate means for the phase meter 53 includes a band pass filter 57 for controlling the gate circuits 58 and 59 in the input circuits of the phase meter. Similarly, the band pass filter 60 controls the gate circuits 6! and 62 for the phase meter 54, the band pass filter 63 controls the gate circuits 54 and 65 for the phase meter 55, and the band pass filter 66 controls the gate circuits 6'! and 68 for the phase meter 55.

As indicated in the drawings, the receiver 46 is fixed tuned to a center frequency of 1700 kilocycles and is designed to accept the carrier waves radiated by either of the transmitters H4 or 26, 1

whether modulated or unmodulated; the receiver dB is fixed tuned to a center frequency of 1798 kilocycles and is designed to accept the carrier waves radiated by either of the transmitters is or 27, whether modulated or unmodulated; and

the receiver 47 is fixed tuned to a center frequency of 1752 kilocycles and is designed to accept the carrier waves radiated by either of the transmitters I5, or 25.

The various band pass filters employed in the transmitting units it and I2 and in the receiving unit It are sharply tuned audio filters which may be of any standard commercial construction, and the phase meters 53, 54, 55 and 56 may likewise be of standard construction although they are preferably of the type disclosed in Hawkins et a1. Patent No. 2,551,211 issued May 1, 1951. As more fully described in the prior Hawkins et a1. Patent No. 2,513,318 issued July 4, 1950, the use of sharply tuned audio filters for separating the various position indicating and reference signals, may cause phase shift difiiculties due to differing frequency response characteristics of the filters. It will be observed, however, that in the system illustrated in Figs. 1 and 2, the sharply tuned audio filters are employed only in the control circuits for the gates rather than in the circuits for the signals which are to be phase compared. Various types of gate circuits may be employed in systems embodying the present invetnion so long as the gate circuits selected provide a distortionless wide pass band, and in Fig. 3 there is shown a suitable gate circuit which is identified, for example, as the gate circuit 34a at the transmitting unit 10. As shown in Fig. 3, the gate circuit includes a suitable input and isolating transformer 69, the primary winding of which is connected to the input terminals 70 of the gate circuit 34a and the secondary winding of which is connected to the grids of a pair of three-element electron discharge devices H and 12 which are connected in push-pull relation and biased for class A operation. The anode-cathode circuits of the tubes II and 72 are connected, as shown, to the primary winding of an output transformer 13, the secondary winding of which is connected to the output terminals 14 of the gate circuit 34a. Normally, the tubes H and 72 are biased beyond cutoff as, for example, by a battery 15 connected to the cathodes of the tubes so that no signal will pass from the input terminals to the output terminals of the gate circuit. The gate circuit, however, includes a pair of control terminals 76 which are connected for energization from the 510 cycle band pass filter 34b and, as shown in Fig. 3, these terminals are connected to the primary winding of a, control transformer 11, the secondary winding of which is connected to a full wave rectifier comprising the two element tubes 78 and 19, the rectifier circuit also including a suitable cathode load resistor 80 and a bypass condenser 8 i As shown, one end of the load resistor 80 is connected by a suitable conductor 82 to a mid tap 83 on the secondary winding of the input transformer 59 which supplied the grids of the tubes H and 72. Thus, whenever a 510 cycle signal is supplied through the band pass filter 34b to the control terminals 76 of the gate circuit 34a, a rectified positive voltage will be applied to the grids of the tubes H and 72 so as to reduce the negative bias on the tubes to the proper value for class A operation and any signals supplied to the input terminals 70 will be conducted through the gate circuit without distortion to the output terminals 74.

Gonsidering now the operation of the system shown in Figs. 1 and 2, when the commutating ring 29 is in the position shown in Fig. 1, anode current will be supplied to the transmitter 25 and the 1700.00 kilocycle wave radiated by the transmitter will, as indicated by the solid line arrow 8d, be radiated to and accepted by the receiver 35 at the transmitting unit :2, together with the 1700.330 kilocycle wave radiated from the transmitter 14 at the transmitting unit :9, the latter wave being indicated by a solid line arrow $5. The beat frequency of 330 cycles between the two carrier waves accepted by the receiver 39 is reproduced in the audio frequency section of the receiver and delivered through the 330 cycle band pass filter Mb to the input terminals of the rectifier and control tube at. The rectifier and control tube is of the type well known in the art and is effective when selectively energized and deenergized to close and open the energizing circuit for the winding of the control relay 2!. As is apparent from the drawing, the relay 2i includes a pair of normally closed contacts 87 which normally complete the anode current circuit for the electron discharge tubes of the transmitter 20 and a pair of normally open contacts 88 which are effective when the relay 2| is operated to close the normally open anode current circuit for the electron tubes of the receiver 30. Accordingly, it will be apparent that by virtue of the production of the 330 cycle beat note signal at the receiver 39, the relay 2! is operated to render the transmitter 20 inoperative and to render the receiver 40 operative.

In addition to the above described control operation, the 330 cycle signal is transmitted through the band pass filter 41b to the control terminals of the gate circuit ila, so as to render the gate conductive. As shown in Fig. 1, the receiver 89 also supplies the 330 cycle signal produced therein to the switch means 45 which is connected between the receiver and the input terminals of the gate circuit 41a, and since the contact arm is being driven at a constant predi iiermined speed the 33(), cycle signal will be pl thrpiighthejswitchv and the conductive ge esis-tome mbdmatdr, 2 3, during the port orf offfeac'h, rotation of the contact arm that the arm in, contact with the conducting segment 'Infadditionj to the transmitters Hi and 26, the trah'smittr's' 25 and i5, are operative during th h port on of the cycle of operation, the conhan offthe control relay its at the unit Hi being, closedv so as to render the transmitter 55 operative, and the relay contacts Q being open steers render the receiver 33 at; the unit iii inoperative, The 1752x120 kilocyi le carrier wave e'd'by the transmitter l and the 1752.00 he, car ier wave ra ated y t e ans: as respectively indicated by the solid un t 91' nd 92, a e ra i ed o and e cpted by the receiver 40 at the unit l2 and the bcatjfrfiiilli cy of 420 cycles between-the two earner" waves isreproduced in the audio freduenc'y sect dn of the receiveriq and supplied, as "dicatedftothe input terminals of the mixer t; which, as shown, is also supplied with the 33(} cycle signal produced in the receiver 39. In the r'niife'r the twosignals are heterodyned to produ "a beat frequency diiference signal of 90 es which is supplied through the low pass t r was? s i iior in during e phrtions of each rotation of the contact arm ied thatthe arm engages the segment 35b the 90 cycle signal 'wil l be supplied through the conducti ve gate circuit did to the modulator 23. Thus, it will b seen that during this cycle of operation of the system, the 1793.510 kilocycle ea ner wave radiated by the transmitter 99 will befal ernately modulated with the 330 cycle and 90 cydebeat' fred fiency 'signals, and this carrier wave is radiated to the mobile receiving unit 13 as'in' cat'ed'bythe solid line arrow at ers it is accepted by the receiver 48. At the same time that the modulated carrier wave representedby the solid line arrow 93 is "being received at the receiving unit, a pair of'carri'er waves from the transmitter is and the transmitter 25 are being radiated to and accepted by the receiver :51 at the receiving unit 53, as indicated by the solid line arrows $4 and 95, and similarly, as represented by the solid line arrows 95' and 91, the carrier w'aves radiated by the transmitter is and the'transmittefZEi, are being radiated to and accepted by the receiver'fifi at the receiving unitl3.

At the receiving unit !3, the beat frequency of 330 cycles which exists between the carriers from the transmitters I 4 and 25 represented by the solid'line arrows 96 and 91, is reproduced in the audio frequency. section of the receiver 46 and is supplied to the left hand or input terminals of the normally closed gate circuit 52. At the same time, the 330 cycle. and 9.0 cycle reference signals which are. modulated on the carrier wave radiated from the transmitter l9 and represented by the solid'line arrow 93, will be reproducedin the receiver 413 and alternately appear at the output term nals. of the receiver. During the periods when the contact arm 45d of the switch as is in engagement with the conducting segment 45a the 330 cycle reference signal will be supplied through the 330 cycle band pass filter fiflto the controlterminals of the gate circuits 6! andt; so as to render these gate circuits cohdnctive. Since this 330 cycle reference signal is also sup:- plied to the input terminals of'the gate 61, the two 330 cycle signals will pass" through the -gates BI and 62 to the opposite terminals "ofthe phase meter 54, which phase meter functions to measwe the phase relationship between the 330 'cyc1e position indicating signal from the receiver 46 and the 330 cycle reference signal from the receiver 48, thereby providing a position. indication of the mobile unit l3 relative to the transmitting units it and H. Although the signals are supplied to the phase meter in the form of short pulses, these pulses will be of sufficient rapidity to cause a continuous indication on the phase meter.

As previously indicated, the phase sensitivity of the position indication thus obtained, is determined by the mean or average frequency of the radiated waves and since the mean or average frequency of the carrier waves radiated by the transmitters Hi and 26 is 1700.165, the iso-phase lines representative of the same phase relation-' ship between the standing waves produced by the transmitters H3 and 26 along a line joining the units IE) and H would be spaced apart a distance of approximately 290 feet. This may be consid ered as the fine or high phase sensitivity position indication with respect to the transmitting units H3 and I I Simultaneously, with the above described en ergization of the phase meter 5% to provide this fine position indication, the receiver at the unit i3 is effective to reproduce in the audio fre-' quency section thereof the 420 cycle beat frequency difference between the waves radiated by the transmitters l5 and 25 so as to produce in the output of the receiver 4], a 420' cycle'beat frequency signal which is supplied to the mixer or heterodyne means 49 which is also supplied, as shown, with the 330 cycle beat frequency signal developed at the receiver dfiias previously de scribed. In the mixer $9, a 9}) cycle position indi eating signal is produced which passes through the low pass filter 5| to the left hand or input terminals of the gate 6}}. During the intervals in which the cycle reference signal appears at the output of the receiver 48,1. e. when the contact arm 45d engages the conducting segment 4 5b, this 90'cycle reference signal passes through the band pass filter ft to'the control terminals of the gate circuits l5! and 68 so as to render these gates conductive. The input terminals of'the'gate circuit 5 1 are connected, as shown, to the output terminals of the receiver '48, and accordingly, whenever the gates 61 and 63 are rendered conductive the 90 cycle position indicating signal from the mixer :89 and the 90 cycl reference sig nal from the receiver 48 are supplied through the conducting gates 'tothe phase meter 55' for phase comparison. As previously'indicated, the phase sensitivity of the 90 cycle position indicating and reference signals is determined bythe ratio between the mean frequencies ofthe waves transmitted by the pair of transmitters Man'd 2161 from which the 330' cycle beat frequency sig a was produced and the pair of" transmitters Edand 25 from which the 420 cycle beat frequency signal was produced. Since; with respect toeach of these pairs of transmitters, thetransrhitter' at the unit It] is of higher frequency than the transmitter at the unit"! 8, thereby providing a phase shift'of the same sense ineachof the'bat fire quency signals, heterodynin the 330 cycle and 420 cycle'beat frequency signals the mixer a p d ce n l tr it is a the hase. o wh h Will vary by the diiference'between the 1700.165 kilhcycle meanfrequency of the transmitters IA an afi iihe 52-219 i s-lei i e n i q as of th transmit e s 5sec?? a th r words, the phase sensitivity of the 90 cycle position indicating signal supplied to the phase meter will correspond to a carrier signal of approximately 52.645 kilocycles which may be termed a phantom frequency equal to the difierence between the real mean frequencies. Thus, when the 90 cycle position indicating signal is phase compared with the similarly produced 90 cycle reference signal supplied from the receiver 48, a much smaller number of lanes or 360 phase coincidences between the transmitting units 50 and i i will be obtained and these iso-phase lines will be spaced apart along the line joining the units 50 and ii, a distance equal to one-half the wave length oi a wave having a frequency of 52.045 hilocycles or a distance of approximately 2500 feet. It will thus be observed that the phase meters at and 55 provide two position indications of different sensitivity indicative of the position of the mobile receiving unit I3 relative to the transmitting units 553 and Ii. lhe low phase sensitivity reading obtained from the phase meter '56 may thus e employed to establish within which of the pairs of iso-phase lines spaced 2% feet apart and indicated by the phase meter 5 the mobile receiving unit 53 is positioned.

It will be observed that during the above described transmitting interval, the phase meters 53 and 55 are completely isolated from the receiver output circuits by the associated gate circuits, there being no 90 cycle or 510 cycle signal present in the output circuit of the receiver ii-3, which is necessary to render these gates conductive through the band pass filters all and 3. Vfhile the switch 35 at the transmitting unit 52 may be operated at any desired speed, it is desirable to select a speed that will insure at least one pulse of each of the 330 cycle and 90 cycle signals during each half cycle of operation produced by the commutator ring 29 at the transmitting unit H. For example, with the commutator ring 29 operating at ten revolutions per second as previously indicated, the switch s5 is preferably driven at some speed in excess of thirty revolutions per second. Furthermore, in order to cause the phase meters 55 and 55 to operate at substantially the same speeds in indicating position changes, the relative lengths of the conducting segments 45a and 552) of the switch is should be so proportioned that the period during which the 90 cycle reference signal is being transmitted bears to the period during which the 330 cycle reference signal is being transmitted the same ratio as the sensitivity of the coarse phase indication bears to the sensitivity of the line phase indication, i. e. approximately 1 to 35.

At the end of the above described transmitting interval, the commutating ring 29 functions to interrupt the anode current circuits to the transmitter 26 thereby terminating operation of the phase meters 5d and 56 by reason of the fact that the 1700 kilocycle carrier wave from the transmitter 26 is no longer radiated to the receiver "it at the mobile receiving unit I 3 or to the receiver 39 at the transmitting unit I2 which causes the 330 cycle signals developed at these receivers to disappear. Disappearance of the 330 cycle signal at the receiver 39 deenergizes the control tube t2 and consequently relay 25 operates to its normal position in which the receiver i0 is rendered inoperative and the transmitter 20 is rendered operative through closure of its anode current circuits. Disappearance of the 330 cycle signal at the transmitting unit I2 is also efiective to render the gate circuit Ma non-conductive so as to prevent further modulation of the carrier wave radiated by the transmitter I9. Although the 420 cycle signal developed at the receiver 41 at the receiving unit I3 will not be interrupted immediately that signal alone cannot effect operation of any of the phase meters. A short time interval after operation of the transmitter 26 is stopped, the commutating ring 29 functions to deliver anode current to the tubes of the transmitter 21 thus rendering this transmitter operative.

As soon as the transmitter 21 is rendered 0perative, the 1798.00 kilocycle carrier wave radi ated by this transmitter together with the 1798.510 kilocycle carrier wave radiated by the transmitter I9 will be accepted at the receiver 32 of the transmitting unit I0, as indicated by the broken line arrows 98 and 99 respectively. This receiver 32 functions to produce in its output circuit the 510 cycle beat frequency difference between these carrier waves and this 510 cycle signal is supplied through the band pass filter 34b to the rectifier and control tube 35 so as to operate the relay Ilia which accordingly operates, as previously indicated, to render the transmitter I5 inoperative and render the receiver 33 operative. In addition, the 510 cycle heat frequency signal is supplied from the band pass filter 34b to the gate circuit 34a thereby rendering the gate circuit conductive, and the 510 cycle beat frequency signal which is also supplied to the input terminals of the gate circuit is thus conducted through the gate and the cyclically operating switch 38 to the modulator IT for modulation on the carrier Wave radiated by the transmitter I4.

As soon as the receiver 33 at the transmitting unit I0 is rendered operative, it becomes effective to accept the 1752.00 kilocycle carrier wave radiated by the transmitter 25 and the 1752.420 kilocycle carrier wave radiated by the transmitter 20 at the transmitting unit I2, these carrier Waves being respectively represented by the broken line arrows 00 and WI. The receiver 33 functions to produce in its output circuits the 420 cycle beat frequency signal representing the frequency difierence between these last mentioned carriers and this 420 cycle signal is supplied to the mixer 36 which is also supplied with the 510 cycle signal produced at the receiver 32, and the mixer thereby functions to produce at its output circuits a cycle beat note or difierence frequency, which is selected by the low pass filter 31 and supplied through the switch means 38 and the conducting gate 34a to the modulator I? for modulation on the carrier wave radiated by the transmitter I4.

Thus, the wave radiated by the transmitter I4, which is indicated by the broken line arrow I02, extending from the transmitter I4 to the receiver 55 at the mobile receiving unit I3 is alternately modulated with 510 cycle and 90 cycle reference signals. Simultaneously, with the production and transmission of these reference signals, the carrier waves radiated by the transmitters 25 and 2c are radiated to and accepted by the receiver 6'! at the mobile receiving unit as represented by the broken line arrows I03 and I04, and the carrier signals respectively radiated by the transmitters 2'! and I 9 are radiated to and accepted by the receiver 48 at the mobile receiving unit as represented by the broken line arrows I05 and I06 respectively.

A e e v ng u it I3, the operation is identical with. that. described. in connectionv with. the firsthalf cycle ofoperation.exceptjthatthephasce meters 5.3and 55 are nowv operatedftoprovidefine and coarse position indications ofthe. position of the mobile receiving unit. lf3 relative. to, the transmittingunits II and l2.. Thus,.the 510' cycleand 90 cycle. modulation components are alternately reproduced at the receiver 45.. andthehldcycle signal. issupplied through theband passfilter 5.7 to. the control terminals of the. gates. 58 and 59 thereby rendering. the gates, conductive during the periods when the 510' cycle signal is being transmitted, and. at thesame time. a difference frequency. of 510 cycles isproduced at the re,- ceiver AB. The two. 510v cycle. signalspass through thev conducting gates to the. phase meter 53 for phase comparison. Thus, a. fine orh gh: ph sensitivity position indication is.produced haying isophase lines spaced apart. approximately 275 feet. At the same-time, the lzocycle difference frequency signal produced! at the-receiver- M is supplied to. the mixer 59 which is also supplied from the receiver 43 with the 5.10 cycle signal-derveloped at that: receiver. At the mixer; 5Q, the two signals areheterodynedi to providea 9.0; cycle difierence; frequency position indicating signal whichpasses through the:low pass filter 524:; the gate 65; During the periods when the 90, cycle reference signal is beingreproduced' in the; receiver 66, this signal passes through the; band pass filter 63: and'is effective to render the gates 64 and 65 conductive whereby the two 90 cycle signals are supplied to the phase meter :5- for phase comparison to provide a, coarse position indication of the position of the mobile receiving unit relative tothe-transmi'tters I. l: and [2' having a low phase sensitivity corresponding. to iso-phase line Is having a spacing of approximtaely 1'0;6il0

It will thus be seen that the phase meters. 5'4 and and the phase meters. 53 and 55 function alternately to provide fine and coarse position indications at the mobile unit Hiwhich. cor-respond to two pairsof intersectingsets of: iso-phase lines of hyperbolic pattern, one pair comprising a hyperbolic grid in which the isoephase: lines are spaced approximately 28.0 feetv apart: along the iso-phase: lines of the respective pairs of transmitters, and the other pair comprising similar patterns in which the isophase;- lines are spaced approximately I0,000. feet apart.

As previously indicated in the description of the operation of the switch means 45: at the transmitting unit I2, the switch. means 3.8 at the unit H) may be operated at any desired speed and the ratio of the lengths of the conducting segments 38b and 3841 should preferably be about 1 to- 35. Furthermore, it should be noted? that it is not necessary to synchronize the operation of the switch means 38 and 45 either: with respect to eachother or with respect to. the commutator ring 29.

It will be observed that in the above described embodiment of the invention, sharply tuned audio frequency band pass filters. have been. en.- tirely eliminated from the signal circuits at both the transmitting units and at the receiving unit, thus obviating the above referred to problems of balancing out undesirable phase shifts that occur in such sharply tuned filters upon slight varia- 114 low, passlfllte s 1... .1 nd... 5 ave Wid -mass. distorti nless haracteristics w i h. o .9. i rise eha hittn oblems- The system of. F gs... and. zfunctio is. Q-Pm vide accurate unambiguous position fixes. and gl er desirable haracter stics. f e. y tem is. the factthat none hesisria a plied. o. the. phase. meters ba s. th o narr and Pass. filters. the. latte be n e u red. to ope te the, gate circuitsonly, andthe fact. that only one. signal at atime is tranfimittedasa modulation component. Eurthermore, the filters, gate means, and. time sharin fac l ties. rev t gn s from being appl edt he ph se meters xc pt those eu zedi r op ratio b he hase-m e h y redu in .or l mv atinsnhase meter. drift...

In. the embodimentof. the invention shownin Figs. sand 5., asimilar. posi on determ in SySf temisrrovided, inwhichsqmewhet difierent. ime sharin h t rodyning. and eating r a em nts areernpleved. Referrinsncw pecifi l taF ss- 4. and. 5,. the nven on s, us rated as em odi d in a. three-focilhyperbolic ontinuouswave sysr.

tem. for. providi g. po ition. n orma on. t.

tions in temperature frequency, etc. --Likewise it will be observed that narrow band pass filters are employed in this system only in the control circuits where phase shift problems are non-ex istent. All of the gate circuits as well as the mobile r ceivin unit. I 1 Fist W ch-m r be carr ed. by. a. ve s l r. behicl per tin wi h the radius of transmissionof. a plurality of, spaced, transmitting units we. L99. nd. Mt- Theseun ar preferably. paced. part si l rly to the units ill, u; and L2; of Fi s. and s s e c bed more. fully, hereinafter, the transmitting units itdand H0 ar qu pped, ontin ou y to r d a n r. f. position. ndicat ng; s na s n. he fo m of, carrier. Waves of different. frequen e and to intermittently qr alternatel r d atea e ond pair f carrier war sof. sti ldi er nt r uencies,- On the other. hand. t etra s it ing. un W9; s equipped to continuously radiate av carrier wave f oth r frequ nc and alternately. o iate an additional pair of position. indicating signals in. the form of carrier waves of still diiierentfreqnencies.

Specifically, the transmitting unit. 19,3. come. prises, a continuously operativetransm-itter [H and a transmitter H2 wh ch s a ap d t e a ternately nde d per ive a d nop r ive y a suitable. lay He. he tr nsm tt r Z. is adap ed t radiate. a con in us carr er Wav a a. trequency of 1752.429: kilocycles and the trans: mitter ti I. consists= 0i 9. Carrier wave oscillator Mt. ad pted. for erati n t a re uenc f 1700.330 kilocycles, a modulator 1.2.5, and a power amplifi r. Ht where y the outpu f an mitter HI constitutes. a continuous. carrier Wave, which, as. is. mo e fully described. her f r. may have suitabl modula n signal mo a thereon during certain periods of the. transmitter operation. Similarly, the. transmitting unit lie comprises. a. Continuously operative transmitter i. H and a transmitter l 18. which is adapted to. be alternately rendered operative and inoperative by as-uitable relay l 19,-. Thetranszmitter I 18 when rendered operative by therelay, radiates a continucus carrier wave. at a irequency or 1152.600 kilocycles and the transrmtter ll'l includes a carrier wave oscillator Hit a a ted: f r o e a i a a freq n y of 98-510 kilcc les. a m u a o [=2- l and a power amplifier I22 whereby the output of the transmitter Ill constitutes a continuous carrier wave which, as. is more fully described hereinafter, may have suitable modulation signals modulated he on u ing certa peri d f noration.

The tra smitti unit Hi9- is. d n i a in con.- struction and operatio with the transm tting unit II of Fig. 1 and, as shown, includes a continuously operative transmitter I23 and a pair of alternately operative transmitters I24 and I25 controlled by a continuously driven commutating ring I26.

Referring again to the transmitting unit I03, this unit comprises, in addition to the transmitters III and II2, a pair of fixed tuned receivers I21 and I28, a frequency responsive gate means I29, 2. rectifier and control tube unit I for controlling the relay II3, and a cyclically operable switch means I3I. The gate means I29, in addition to a suitable gate circuit I290. which may be identical with the gate circuit 34a shown in Fig. 3, includes a 510 cycle band pass filter I291). The switch means I3I comprises a commutating ring made up of a narrow conducting segment I3Ia and an insulating segment I3Ib adapted to be driven at a constant speed by a suitable driving unit I32 and which cooperates with a contact brush I3Ic intermittently to supply signals from the receiver I21 to the input terminals of the gate circuit. All of the above described equipment which goes to make up the transmitting unit I08 is connected as shown in Fig. 4 of the drawing, as will become clearly apparent in the description of the operation.

The transmitting unit III} which is substantially identical with the transmitting unit I08 except for the frequencies at which various pieces of equipment operate, includes, in addition to the transmitters Ill and H8, a pair of fixed tuned receivers I33 and I34, a frequency responsive gate means I35, a rectifier and control tube unit I35, and a cyclically operable switch means I31 which is identical with the switch means I3! at the transmitting unit I08 and is driven by a driving unit I38. The gate means I35 includes, in addition to a suitable gate circuit I35a, a 330 cycle band pass filter I35b.

Referring now to Fig. 5, the mobile receiving unit I01 is shown as comprising a plurality of fixed tuned receivers I39, I and MI, of which the receivers I39 and MI are of the amplitude modulation type, a plurality of mixers or heterodyning means I42, I43, I44 and I45, a plurality of 90 cycle band pass filters 6,141, I48 and I49, and a plurality of phase measuring means or phase meters I50, I5I, I52 and I53. Associated with each of the phase meters I and I5I are a plurality of normally closed frequency responsive gate means each of which includes a suitable sharply tuned narrow band pass filter and a plurality of gate circuits. Specifically, the gate means for the phase meter I 59 includes a pair of band pass filters I54 and I55 for respectively controlling the normally closed gate circuits I58 and I5? and the normally open gate circuits I53 and I59 in the input circuits of the phase meter. Similarly, the band pass filters I60 and IBI respectively control the normally open gate circuits I32 and I53 and the normally closed gate circuits I54 and I for the phase meter I52.

As indicated in the drawings, the receiver I39 is fixed tuned to a center frequency of 1700 kilocycles and is designed to accept the carrier waves radiated by either of the transmitters I II or I24, whether modulated or unmodulated; the receiver I4I is fixed tuned to a center frequency of 1798- kilocycles and is designed to accept the carrier waves radiated by either of the transmitters II! or I25, whether modulated or unmodulated; and the receiver I40 is fixed tuned to a center frequency of 1752 kilocycles and is designed to accept the carrier waves radiated by any of the transmitters II2, I23 or H8. The normally closed gate circuits employed at the receiving unit I91 may be of the type shown in Fig. 3, and a suitable "type of normally open gate circuit is shown in .Fig. 6 and identified as the gate circuit I58, for example. As shown in Fig. 6, the gate circuit includes a suitable input and isolating transformer I66, the primary winding of which is connected 'to the input terminals I51 of the gate circuit I59 :and the secondary winding of which is connected to the grids of a pair of three-element electron discharge devices I38 and I59 which are connected in push-pull relation and biased for class .A operation. The anode-cathode circuits of the tubes I58 and I69 are connected, as shown, to the primary winding of an output transformer I10, the secondary winding of which is connected to the output terminals I'II of the gate circuit. Normally, the tubes I58 and I59 are biased for ezlass A operation as, for example, by a battery I 12 connected to the cathodes of the tubes, and consequently, signals will pass from the input terminals to the output terminals of the gate circuit. The gate circuit, however, includes a pair of control terminals I13 which are connected for energization from the 420 cycle band pass filter I55 and, as shown in Fig. 6, these terminals are connected to the primary winding of a control transformer I14, the secondary winding of which is connected to a full wave rectifier comprising the two-element tubes I15 and I15, the rectifier circuit also including a suitable cathode load resistor I11 and a bypass condenser I13. As shown, one end of the load resistor I11 is connected by a suitable conductor I19 to a mid tap I05 on the secondary winding of the input transformer I14 which supplies the grids of the tubes I55 and IE9. Thus, whenever a 420 cycle signal is supplied through the band pass filter I55 to the control terminals I13 of the gate circuit I58, a rectified negative voltage will be applied to the grids of the tubes I68 and IE9 so as to increase the negative bias on the tubes to a value beyond cut-off, thereby preventing the passage through the gate circuit of signals supplied to the input terminals.

Considering now the operation of the system shown in Figs. 4 and 5, when the commutating ring I26 is in the position shown in Fig. 4, anode current will be supplied to the transmitter I24 and the 1700.00 kilocycle wave radiated by the transmitter will, as indicated by the solid line arrow I 8|, be radiated to and accepted by the receiver I33 at the transmitting unit I I5, together with the 1700.330 kilocycle wave radiated from the transmitter I II at the transmitting unit M38, the latter wave being indicated by a solid line arrow I02. The beat frequency of 330 cycles between the two carrier waves accepted by the receiver I33 is reproduced in the audio frequency section of the receiver and delivered through the 330 cycle band pass filter I35b to the input terminals of the rectifier. and control tube I35. As will be apparent from the description of the control tube 42 and the associated relay ill of Fig. 1, production of the 330 cycle beat note signal at the receiver I33 is effective to cause operation of the relay II9 to render the transmitter H3 inoperative and to render the receiver I34 operative.

In addition to the above described control operation, the 330 cycle signal is transmitted through the band pass filter I355 to the control terminals of the gate circuit I35a so as to render the gate conductive and since the 330 cycle signal is also supplied to the input terminals of the a circuit theafio c cl si na Millb su th ca rier w r ra ia e vloyth ansmit in. n addit on to th transmit r H a 1 t e mitter J1 an 112 are o er iv du n t i o tio .of th cyc of operati n. the contacts I. 93 -of the ,control relaylltat the unit I98 being closed so. as ,torenderthe ;trans mitter I I2 operative, and-the relay, contacts i843 being open so .as-to render the receiver I2I at the unit I08 inoperative. The 1752.420 kilocycle carrier wave radiated bythe transmitter H2 and the 1'752,00, -k;ilocycle ,carrier wave radiated by the .transmitter I23 as respectiv l indicated by the solid. line arrows .118 and 18. are radiated to and acceptedbythe receiver I36 at the unit jifl andthe beat frequency of 420 cycles between-thestwo carrier ,waves is re- .produced in the audio frequency section of the receiver I34 and :supp1ied,,,as indicated, ,to the input terminals of the conductive vagate {35c thrcughthe conductive se ment .1371: and the brush contact 1310 of the cyclicallyoperating switch means. Accordingly, duringthe portions of each rotation ofthe commutator ring It! that the contact 1310 engages :the segment I 31a the .420 cycle signal-will be supplied through the conductive gate'circuit :to the modulator 1.2!. Thus, it will be seen that .during this cycle of operation of the system, the 1798.510 kilocycle carrier wave radiated by the transmitter H7 will be constantly modulated with a 330 cycle beat frequency signal and will be intermittently modulated with the 420 .cycle .beat frequency signal, and this carrier ,wave is radiated to the mobile receiving unit 101 as indicated by the solid line arrow I86 where itis accepted by the receiver I4I. At the same time that the modulated carrier wave represented .by the solid line arrow I86 isbeingreceived at the receiving unit, a pair of carrier waves from the transmitter H2 and the transmitter I23 are being radiatedto and accepted by the receiver I40 at the receiving unit I91, as indicatedby the solid line arrows I81 and I88, and similarly, as represented by the solid line arrows I89 and I90, the carrier waves radiated by the transmitter II I and the transmitter I24, are'being radiated .to and accepted by the receiver I39 at the receiving unit I01.

At the receiving unit I111, thebeat frequency of 330 cycles which exists between the carriers from the transmitters HI and I26 represented by the solid line arrows I89 and I99, is reproduced in the audio frequency section of the receiver I39 and is supplied throughthe band pass filter I54 to the control terminals of the normally closed gatecircuits I56 and I5! so as to render these gates conductive. At the same time, the 330 cycle and 420 cycle reference signals which are modulated on the carrier wave radiated from the transmitter II! and represented by the solid line arrow I 96, will be reproduced in the receiver MI and the 330 cycle signal will appear continuously atthe output terminals of the receiver. During periods when only the 330 cycle signal is present this 330 cycle reference signal will be supplied through the normally open gate circuit I59 and the normally closed gate circuit 157 which ishow conductive to the right hand terminals of the phase meter I 59. Since the 330 cycle position signaldeveloped at the receiver ,I-39is also supplied to the input terminals of-the'gate I56, this signal will pass through the gates I56 and 1:58 to the oppos t te m n s f t p as m r 15.0 wh phase rneter functions to measure the phase relationship between the 330 cycle position in- .dicating signal from the receiver 39 and the 330 cycle reference signal from the receiver Ml, thereby providing a position indication of the mobile unit It! relative to the transmitting units m8 and I99. This position indication, as will be apparent from the description of the system f i s- 1 and 2, ma be cons d re as t fine or high phase sensitivity position indication with respect to the transmitting units I98 and 5599, h i 1 91 9 45 l n aceie e i a v 9 feet apart along ,a iine joining these transmitters.

Simultaneously, with theabovedescribed energization pf the phase meter I59 to provide this fine position indication, the receiver M9 at the unit I 91 is effective to reproduce in the audio frequency section thereof the Q20 cycle beat frequency difference between the waves radiated bythe transmitters .I I 2 and I23 so as to produce in the output of the receiver M0, a 420 cycle beat frequency signal which is supplied to the mixer or heterodyne means 1532 which is also supplied through the gate circuit I56 with the 330 cyclebeat frequency signal developed at the receiver I99 as previously described. In the mixer M2, a cycle positionindicating signal is produced which passes through the band pass filter I46 to the left handterminals of the phase meter I-BI.

During the intervals in which both the 420 cycle and the 330 cycle reference signals appear at the outputof the receiver IAI, i. e. when the contact arm I3Ic engages the conducting seg ment I 31a, these two reference signals ,will .be supplied to the m ixer ;I4 5 ,which thereupon func: tions to produce a 9 0 cycle reference signal, and thisQOcycie referencesignal passesithrough the band pass filter I118 to the right hand terminals of the phase meter I5I .for phase comparison with the 90 cycle positionindicating signal.

The 430 cycle referencesignal produced in the receiver I4 inadditionto its above described function, is also ern ployed for the purpose of isolating the hue indication phase meter E59 during the periods when the 420 ,cycle signal is present at the output of the receiver Ml. Thus,

this 420 cycle signal is supplied-through the and pass filter [Stito the control terminals of the normally opengates 1.58 and .159 to render these gatesnon-conductiveas described in connection withiFig. 6. In the,.abs ence of the gates I58 and 159, improper operation of the phase meter I59 would be caused by the .420 cycle re erence signal during the intermittent periods when the coarse indication,phase meter I5l is bei ne zedexplained in connection with Figs. 1 and 2, the phasesensitivitypf the 90 cycle position indicating signal supplied to the. phasemeter I5! will correspond 2 0 a carrier signalof approximate1y52pi5 kilocycles which may,be.termed a phant m requ nc sequel ,to the difference .between the real mean frequencies. Thus, when the 90 cycle signals are phase compared, a much smaller number of ,lanes or .360" phase coincidences betweenthetransmittingunits I08 and its will beobtained .and these iso-phase lines willbespaced apart/along the line joiningthe units I98 and 169, a distance equalto one-half the wave lengthpf'. awave havinga frequency of v52 .045.l-:i1ocycles or. adistanceof approximately 9500feet. It-will-thusbeobserved'that the phase meters I50 and II provide two position indications of different sensitivity indicative of the position of the mobile receiving unit I01 relative to the transmitting units I08 and I09. The low phase sensitivity reading obtained from the phase meter I5I may thus be employed to establish within which of the pairs of iso-phase lines spaced 290 feet apart and indicated by the phase meter I50 the mobile receiving unit I01 is positioned. Furthermore, in order to cause the phase meters I50 and I5I to operate at substantially the same speeds in indicating position changes, the conducting segment I31a of the commutator ring should be so proportioned that the on time of the 420 cycle reference signal bears to the off time of this signal the same ratio as the sensitivity of the coarse phase indication bears to the sensitivity of the fine phase indication, i. e. approximately 1 to 35.

At the end of the above described transmitting interval, the commutating ring I26 functions to interrupt the anode current circuits to the transmitter I24 thereby terminating operation of the phase meters I50 and I5I by reason of the fact that the 1700 kilocycle carrier wave from the transmitter I24 is no longer radiated to the receiver I39 at the mobile receiving unit I91 or to the receiver I33 at the transmitting unit IIO which causes the 339 cycle signals developed at these receivers to disappear. the 330 cycle signal at the receiver I33 deenergizes the control tube I36 and consequently, relay I I9 operates to its normal position in which the receiver I34 is rendered inoperative and the transmitter H3 is rendered operative through closure of its anode current circuits. Disappearance of the 330 cycle signal at the transmitting unit IIO is also efiective to render the gate circuit I351], non-conductive so as to prevent further modulation of the carrier wave radiated by the transmitter I I1.

A short time interval after operation of the transmitter I24 is stopped, the commutating ring I29 functions to deliver anode current to the tubes of the transmitter I25 thus rendering this transmitter operative. As soon as the transmitter I25 is rendered operative, the 1798.00 kilocycle carrier wave radiated by this transmitter together with the 1798.510 kilocycle carrier wave radiated by the transmitter III will be accepted at the receiver I28 of the transmitting unit I09, as indicated by the broken line arrows I9I and I92 respectively. This receiver I28 functions to produce in its output circuit the 510 cycle beat frequency difference between these carrier waves and this 510 cycle signal is supplied through the band pass filter I29b to the rectifier and control tube I30 so as to operate the relay II3 which accordingly operates, as previously indicated, to render the transmitter II2 inoperative and render the receiver I21 operative. In addition, the 510 cycle beat frequency signal is supplied from the band pass filter I29b to the gate circuit I29a thereby rendering the gate circuit conductive, and the 510 cycle beat frequency signal which is also supplied to the input terminals of the gate circuit is thus conducted through the gate to the modulator I I5 for modulation on the carrier wave radiated by the transmitter III.

As soon as the receiver I21 at the transmitting unit I08 is rendered operative, it becomes effective to accept the 1752.00 kilocycle carrier wave radiated by the transmitter I23 and the 1752.600 kilocycle carrier wave radiated by the transmitter H8 at the transmitting unit IIO,

Disappearance of these carrier waves being respectively represented by the broken line arrows I93 and I94. The receiver I21 functions to produce in its output circuits the 600 cycle beat frequency signal representing the frequency difference between these last mentioned carriers and this 600 cycle signal is supplied through the switch means I3I and the conducting gate I29a to the modulator II5 during the periods when the conducting segment I3Ia. engages the contact I3Ic for intermittent modulation on the carrier wave radiated by the transmitter III.

Thus, the wave radiated by the transmitter I I I, which is indicated by the broken line arrow I95, extending from the transmitter I I I to the receiver I39 at the mobile receiving unit I01 is continuously modulated with the 510 cycle reference signals and is intermittently modulated with the 600 cycle reference signals. Simultaneously, with the production and transmission of these reference signals, the carrier waves radiated by the transmitters I23 and H8 are radiated to and accepted by the receiver I at the mobile receiving unit as represented by the broken line arrows I96 and I91, and the carrier signals respectively radiated by the transmitters I25 and H1 are radiated to and accepted by the receiver MI at the mobile receiving unit as represented by the broken line arrows I98 and I99 respectively.

At the receiving unit I91, the operation is identical with that described in connection with the first half cycle of operation except that the phase meters I52 and I53 are now operated to provide fine and coarse position indications of the position of the mobile receiving unit I01 relative to the transmitting units I09 and III Thus, the 510 cycle and 600 cycle modulation components are reproduced at the receiver I39 and the 510 cycle signal is supplied through the normally open gate circuit I52 to the normally closed gate I99, and at the same time a difference frequency of 510 cycles is produced at the receiver I l-I, which is supplied through the band pass filter I6I to the control terminals of the normally closed gates I94 and I55 so as to render these gates conductive. The two 510 cycie signals pass through the conducting gates I34 and IE5 and the normally open gates I52 and IE3 to the phase meter I52 for phase comparison. Thus, a fine or high phase sensitivity position indication is produced having iso-phase lines spaced apart approximately 275 feet. At the same time, the 600 cycle difierence frequency signal produced at the receiver Ids is supplied to the mixture I94 which is also supplied from the receiver I II through the conducting gate I with the 510 cycle signal developed at that receiver. At the mixer I44, the two signals are heterodyned to provide a 90 cycle difierence frequency position indicating signal which passes through the band pass filter I49 to the phase meter I53. During the periods when the 600 cycle reference signal is being reproduced in the receiver I39, this signal passes through the band pass filter I50 and is eifective to render the normally open gates I02 and I63 non-conductive thereby isolating the phase meter I52, and the 510 cycle and 600 cycle are heterodyned in the mixer I43 to provide a 90 cycle reference signal which is supplied through the band pass filter I9! to the phase meter I53. The two 90 cycle signals are thus supplied to the phase meter I53 for phase comparison to provide a coarse position indication of the position of the mobile receiving unit relative to the transmitters I09 and I I0 hav ing a low phase sensitivity correspond n to isophase lines having a spacing of approximately 10,600 feet.

It will thus be seen that the phase meters I50 and and the phase meters [.52 and 153 function alternately to provide fine and coarse position indications at the mobile unit 101 which correspond to two pairs of intersecting sets of iso-phase lines of hyperbolic pattern, one pair comprising a hyperbolic grid in which the isophase lines .are spaced approximately 280 feet apart along the iso-phase lines of the respective pairs of transmitters, and the other pair comprising similar patterns in which the iso-phase lines are spaced approximately 10,000 feet apart.

As previously indicated in the description of the operation of the switch means [3] at the transmitting unit M0, the switch means [3! at the unit we may be operated at any desired speed and the conducting segment I3Ia should preferably be proportioned to give an on-time to off-time ratio of about 1 to 35. Furthermore, it is not necessary in the system of Figs. 4 and 5 to synchronize the operation of the switch means i3} and I3? either with respect to each other or with respect to the commutator ring I26.

As will be apparent from the above description, the phase meter i5] is operative to compare a pair of 90 cycle signals only during the intervals when both a 330 cycle and a 420 cycle signal are being developed at the receiver I41, but the left hand terminals of the phase meter will be supplied with a 90 cycle signal during the entire period in which the 330 cycle signal from the receiver 139 is effective to render the gate I58 conductive. Accordingly, in order to isolate the phase meter 15! except when operation of the phase meter is desired, it may be desirable to introduce a normally closed gate circuit between the band pass filter Hi5 and the phase meter l5! and to control this gate circuit from the output of the band pass filter I48, Similarly a normally closed gate circuit may, if desired, be inserted between the band pass filter I49 and the phase meter 153 and controlled from the output of the band pass filter I47.

While particular embodiments of the invention have been shown, it will be understood, of course, that the invention is not limited thereto since many modifications may be made and it is therefore contemplated by the appended claims to cover any such modifications as fall within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent is:

1. A wave signal transmission system comprising a pair of spaced transmitting units, a plurality of pairs of transmitters for radiating waves of different frequencies, said transmitters of each pair being respectively disposed at different transmitting units, a plurality of hetero dyning means respectively responsive to pairs of signals derived from said pairs of transmitters to produce beat frequency signals having frequencies respectively related to the beat frequencies between the pairs of waves radiated by said pairs of transmitters, other heterodyning means responsive to said beat frequency signals for producing at least one beat frequency reference signal having a frequency related to the beat frequency between at least one pair of said first mentioned beat frequency signals, means for modulating a first one of said beat frequency signals and said reference signal upon one of said radiated waves, normally, closed gate means responsive to one of said beat frequency signals for supplying said first beat frequency signal and said reference signal to said modulating means, and cyclically operating switch means for selectively supplying said first beat frequency signal and said reference signal to said gate means.

2. A wave signal transmission system comprising a pair of spaced transmitting units, a first pair of transmitters including a transmitter at each of said units for radiating a first pair of signals at different frequencies, a second pair of transmitters including a transmitter at each of said units for radiating a second pair of signals at different frequencies, each of said transmitters at one of said units radiating signals of higher frequency than the transmitter of that pair at the other of said units, a pair of heterodyning means respectively responsive to said pairs of signals to produce a pair of beat frequency signals having frequencies respectively representative of the beat frequencies between the signals of said first pair and between the signals of said second pair, other heterodyning' means responsive to said pair of beat frequencysignals for producing a reference signal representative of the beat frequency between said pair of beat frequency signals, means including nor-- mally closed gate means responsive to one of said. pair of beat frequencysignals for modulating one of said beat frequency signals and said ref-- erence signal upon a carrier-for space radiation, and cyclically operating switch means for selectively supplying said last mentioned signals to said gate means.

3. A wave signal transmission system comprise ing a pair of spaced transmitting units, a plurality of pairs of transmitters for radiating wavesof different frequencies, said transmitters of each pair being respectively disposed'at differ-- ent transmitting units, a plurality of heterodyning means respectively responsive to pairs of signals derived from said pairs of transmitters to produce beat frequency signals having frequencies respectively related to the beat frequencies between the pairs of waves radiated by said pairs of transmitters, other heterodyning means responsive to said beat frequency signals for producing at least one beat frequency reference signal having a frequency related to the beat frequency between at least one pair of said first mentioned beat frequency signals, means for modulating a first one of said beat frequency signals and said reference signal upon one of said radiated waves, normally closed gate means responsive to one of said beat frequency signals for supplying said first beat frequency. signal and said reference signal to said modulating means, and cyclically operating switch means for selectively supplying said first beat frequency signal and said reference signal to said gate means, said switch means being effective to supply said reference signal to said gate means for only a small fraction of each cycle.

4. A wave signal transmission system comprising a pair of spaced transmitting units, a first pair of transmitters including a transmitter at each of said units for radiating a first pair of signals at different frequencies, a second pair of transmitters including a transmitter at each of said units for radiating a second pair of signals at different frequencies, each of said transmitters at one of said units radiating signals of higher frequency than the transmitter .of that.

pair at the other of said units, a pair .of. hetero.-

dyning means respectively responsive to said pairs of signals to produce a pair of beat fre quency signals having frequencies respectively representative of the beat frequencies between the signals of said first pair and between the signals of said second pair, other heterodyning means responsive to said pair of beat frequency signals for producing a reference signal representative of the beat frequency between said pair of beat frequency signals, means including normally closed gate means responsive to one of said pair of beat frequency signals for modulating one of said beat frequency signals and said reference signal upon a carrier for space radiation, and cyclically operating switch means for selectively supplying said last mentioned signals to said gate means, said switch means being effective to supply said reference signal to said gate means for only a small fraction of each cycle.

5. A wave signal transmission system comprising a pair of spaced transmitting units, a plurality of pairs of transmitters for radiating waves of different frequencies, said transmitters of each pair being respectively disposed at different transmitting units, means for intermittently operating the said transmitters at one of said units, a plurality of heterodyning means respectively responsive to pairs of signals derived from said pairs of transmitters to produce beat frequency signals having frequencies respectively related to the beat frequencies between the pairs of waves radiated by said pairs of transmitters, other heterodyning means responsive to said beat frequency signals for producing at least one beat frequency reference signal having a frequency related to the beat frequency between at least one pair of said first mentioned beat frequency signals, means including normally closed gate means responsive to one of said pair of beat frequency signals for modulating one of said beat frequency signals and said reference signal upon a carrier for space radiaion, and cyclically operating switch means for selectively supplying said last mentioned signals to said gate means.

6. A wave signal transmission system comprising a pair of spaced transmitting units, a plurality of pairs of transmitters for radiating waves of different frequencies, said transmitters of each pair being respectively disposed at different transmitting units, means for intermittently operating the said transmitters at one of said units, a plurality of heterodyning means respectively responsive to pairs of signals derived from said pairs of transmitters to produce beat frequency signals having frequencies respectively related to the beat frequencies between the pairs of waves radiated by said pairs of transmitters, other heterodyning means responsive to said beat frequency signals for producing at least one beat frequency reference signal having a frequency related to the beat frequencybetween at least one pair of said first mentioned beat frequency signals, means including normally closed gate means responsive to one of said pair of beat frequency signals for modulating one of said beat frequency signals and said reference signal upon a carrier for space radiation, and cyclically operating switch means for selectively supplying said last mentioned signals to said gate means, said switch means being effective to supply said reference signal to said gate means for only a small fraction of eachcycle.

'7. A wave signal transmitting system comprising at least a pair of transmitting units for radiating Waves of different frequencies, means at one of said units for intermittently radiating one of said waves, means at another of said units at least in part responsive to said one wave for developing a first reference signal, means at said other unit for developing a second reference signal, transmitter means at said other unit for radiating another of said waves, means controlled by said first reference signal for rendering said second reference signal means operative and said transmitter means inoperative during intervals when said one wave is being radiated, means for modulating said reference signals upon another wave radiated by said other unit, normally closed gate means responsive to one of said reference signals for supplying said reference signals to said modulating means, and cyclically operating switch means for selectively supplying said first and second reference signals to said gate means.

8. A wave signal transmitting system comprising at least a pair of transmitting units for radiating waves of different frequencies, means at one of said units for intermittently radiating one of said Waves, means at another of said units at least in part responsive to said one wave for developing a first reference signal, means at said other unit for developing a second reference signal, transmitter means at said other unit for radiating another of said waves, means controlled by said first reference signal for rendering said second reference signal means operative and said transmitter means inoperative during intervals when said one wave is being radiated, means for modulating said reference signals upon another wave radiated by said other unit, normally closed gate means responsive to said first reference signal for supplying said reference signals to said modulating means, and cyclically operating switch means for selectively supplying said first and sec-0nd reference signals to said gate means.

9. A wave signal transmitting system comprising at least a pair of transmitting units for radiating waves of different frequencies, means at one of said units for intermittently radiating one of said waves, means at another of said units at least in part responsive to said one Wave for developing a first reference signal, means at said other unit for developing a second reference signal, transmitter means at said other unit for radiating another of said waves, means controlled by said first reference signal for rendering said second reference signal means operative and said transmitter means inoperative during intervals when said one wave is being radiated, means for modulating said reference signals upon another wave radiated by said other unit, normally closed gate means responsive to one of said reference signals for supplying said reference signals to said modulating means, and cyclically operatmg switch means for alternately supplying said first and second reference signals to said gate means.

10. A wave signal transmitting system comprising at least a pair of transmitting units for radiating waves of different frequencies, means at one of said units for intermittently radiating one of said waves, means at another of said units at least in part responsive to said one wave for developing a first reference signal, means at said other unit for developing a second reference Signal, transmitter means at said other unit for radiating another of said waves, means controlled by said first reference signal for rendering said second reference signal means operative and said transmitter means inoperative during intervals when said one Wave is being radiated, means for modulating said reference signals upon another wave radiated by said other unit, normally closed gate means responsive to said first reference' signal for supplying said reference signals to said modulating means, and cyclically operating switch means for alternately supplying said first and second reference signals to said gate means.

11. A wave signal transmitting system comprising at least a pair of transmitting units for radiating waves of different frequencies, means at one of said units for intermittently radiating one of said waves, means at another of said units at least in part responsive to said one wave for developing afirs't reference signal, means at said other unit for developing a second reference signal, transmitter means at said other unit for radiating another of said waves, means controlled by said first reference signal for rendering said second reference signal means operative and said transmitter means inoperative during intervals when said one wave is being radiated, means for modulating said reference signals upon another wave radiated bysaid other unit, normally closed gate means responsive to one of said reference signals for supplying said reference signals to said modulating means, and cyclically operating switch means for selectively supplying said first and second reference signals to said gate means, said switch means being effective to supply said second reference signal to said gate means for only a small fraction of each cycle.

12. A wave signal transmitting system comprising at least a pair of transmitting units for radiating Waves of different frequencies, means at one of said units for intermittently radiating one of said waves, means at another of said units at least in part responsive to said one wave for developing a first reference signal, means at said other unit for developing a second reference signal, transmitter means at said other unit for radiating another of said waves, means controlled by said first reference signal for rendering said second reference signal means operative and said transmitter means inoperative during intervals when said one wave is being radiated, means for modulating said reference signals upon another wave radiated by said other unit, normally closed gate means responsive to said first reference signal for supplying said reference signals to said modulating means, and cyclically operating switch means for selectively supplying said first and second reference signals to said gate means, said switch means being eifective to supply said second reference signal to said gate means for only a small fraction of each cycle.

13. A wave signal transmitting system comprising at least a pair of transmitting units for radiating waves of different frequencies, means at one of said units for intermittently radiating one of said Waves, means at another of said units at least in part responsive to said one wave for developing a first beat frequency reference signal, receiver means at said other unit for developing from a pair of said radiated Waves a second beat frequency signal, heterodyning means responsive to said first and second beat frequency signals for developing a second reference signal, normally operative transmitter means at said other unit for radiating another ofsaid waves, means controlled by said first reference signal for rendering said receiver means operative and said transmitter means inoperative during intervals when said one wave is being radiated, means for modulating said first and second reference signals upon a common carrier, normally closed gate means responsive to one of said reference signals for supplying said reference signals to said modulating means, and cyclically operating switch means for selectively supplying said first and second reference signals to said gate means.

14. A wave signal transmitting system comprising at least a pair of transmitting units for radiating waves of different frequencies, means at one of said units for intermittently radiating one of said waves, means at another of said units at least in part responsive to said one wave for developing V a first beat frequency reference signal, receiver means at said other unit for developing from a pair of said radiated waves a second beat fre-. quency signal, heterodyning means responsive to said first and second beat frequency signals for developing a second reference signal, normally operative transmitter means at said other unit for radiating another of said waves, means controlled by said first reference signal for rendering said receiver means operative and said transmitter means inoperative during intervals when said one wave is being radiated, means for modulating said first and second reference signals upon a common carrier, normally closed gate means'responsive to one of said reference signals for supplying said reference signals to said modulating means, and cyclically operating switch means for selectively supplying said first and second reference signals to said gate means, said switch means being efiece tive to supply said second reference signal to said gate means for only a small fraction of each cycle.

15. Wave signal receiving apparatus for translating received space radiated signals into position indications comprising, a plurality of receivers for respectively receiving pairs of space radiated signals and for heterodyning said received pairs to produce beat frequency signals having frequencies respectively representative of the beat frequencies between the signals of each pair, heterodyning means responsive to said beat frequency signals in pairs for producing a pair of position indicating heterodyne signals having frequencies respectively representative of the beat frequency between the beat frequency signals of said pairs, means for receiving and reproducing a plurality of reference signals having frequencies respectively equal to two of said beat frequency signals and said pair of heterodyne signals, a plurality of phase measuring means for measuring the phase relationship between said two beat fre quency signals and two of said reference signals of corresponding frequency to provide position indications of one sensitivity and between said heterodyne signals and the other two reference signals of corresponding frequency to provide separate position indications of another sensitivity, and a plurality of normally closed gate means disposed in the input circuits of said phase measuring means and respectively responsive to said reference signals for energizing said phase measuring means with signals of matching frequency for phase comparison.

16. Wave signal receiving apparatus for translating received space radiated signals into position indications comprising, a plurality of wave signal receivers for respectively receiving pairs of space radiated signals and for heterodyning said pairs to produce first and second beat frequency signals having frequencies respectively representative of the beat frequencies between the signals of said pairs, said first beat frequency signal constituting a first position-indicating heterodyne signal, heterodyning means responsive to said first and second beat frequency signals for producing a second position-indicating heterodyne signal having a frequency representative of the beat frequency between said first and second beat frequency signals and having a phase sensitivity different from that of said first heterodyne signal, means for receiving and reproducing first and second reference signals having frequencies respectively equal to the frequencies of said first and second heterodyne signals, phase measuring means for respectively measuring the phase relationship between corresponding heterodyne and reference signals to provide separate position indications of different sensitivity, normally closed gate means responsive to said first reference signal for supplying said first heterodyne and reference signals to one of said phase measuring means, and normally closed gate means responsive to said second reference signal for supplying said second heterodyne and reference signals to a second of said phase measuring means.

17. Wave signal receiving apparatus for translating received space radiated signals into position indications comprising, a plurality of wave signal receivers for respectively receiving pairs of space radiated signals and for heterodyning said pairs to produce first and second beat fre quency signals having frequencies respectively representative of the beat frequencies between the signals of said pairs, said first beat frequency signal constituting a first position-indicating heterodyne signal, heterodyning means responsive to said first and second beat frequency slgnals for producing a second position-indicating heterodyne signal having a frequency representative of the beat frequency between said first and second beat frequency signals and having a phase sensitivity different from that of said first heterodyne signal, means for receiving and reproducing first and second reference signals modulated upon a common carrier wave and having frequencies respectively equal to the frequencies of said first and second heterodyne signals, said second reference signal being in the form of short pulses the duration of which bears the same ratio to the time between pulses as the ratio between the phase sensitivites of said first and second heterodyne signals, phase measuring means for respectively measuring the phase relationship between corresponding heterodyne and reference signals to provide separate position indications of different sensitivity, normally closed gate means responsive to said first reference signal for supplying said first heterodyne and reference signals to one of said phase measuring means, and normally closed gate means responsive to said second reference signal for supplying said second heterodyne and reference signals to a second of said phase measuring means only during said pulses of said second reference signal, whereby said phase measuring means operate at substantially equal speeds to provide fine and coarse position indications.

18. A wave signal receiving apparatus for translating received space radiated waves into position indications, comprising a first receiver for receiving a first pair of space radiated waves and for heterodyning said waves to produce a first position indicating signal having a frequency related to the difference frequency between said pair of waves, a second receiver for receiving and heterodyning a'second pair of radiated waves to produce a second position indicating signal having a frequency related to the difference frequency between said second pair of waves, a third receiver alternately operative to receive and heterodyne third and fourth pairs of waves to produce heterodyne signals having frequencies respectively related to the difference frequencies of said third and fourth pairs, heterodyne means responsive to said first position indicating signal and said third heterodyne signal for producing a third position indicating signal, other heterodyne means responsive to said second position indicating signal and said fourth heterodyne signal for producing a fourth position indicating signal, said first receiver being operative when said third receiver is receiving said fourth pair of waves to receive and reproduce first and second reference signals modulated on a common carrier and respectively having frequencies equaling the frequencies of said second and fourth position indicating signals, said second receiver being operative when said third receiver is receiving said third pair of waves to receive and reproduce third and fourth reference signals modulated on a common carrier and respectively having frequencies equaling the frequencies of said first and third position indicating signals, whereby four pairs of matching-frequency reference and position indicating signals are alternately produced in sets of two, a plurality of phase measuring means for respectively measuring the phase relationship between said matching frequency pairs, normally closed gate means coupled to the input circuits of each of said phase measuring means for normally isolating said phase measuring means, said gate means being respectively responsive to said reference signals for supplying said matching signals to said phase measuring means for phase comparison.

19. A wave signal receiving apparatus for translating received space radiated waves into position indications, comprising a first receiver for receiving a first pair of space radiated waves and for heterodyning said Waves to produce a first position indicating signal. having a frequency related to the difference frequency between said pair of waves, a second receiver for receiving and heterodyning a second pair of radiated waves to produce a second position indicating signal having a frequency related to the difference fre" quency between said second pair of waves, a third receiver alternately operative to receive and heterodyne third and fourth pairs of waves to produce heterodyne signals having frequencies respectively related to the difference frequencies of said third and fourth pairs, heterodyne means responsive to said first position indicating signal and said third heterodyne signal for producing a third position indicating signal having a phase sensitivity different than the phase sensitivity of said first position indicating signal, other heterodyne means responsive to said second position indicating signal and said fourth heterodyne signal for producing a fourth position indicating signal having a phase sensitivity different than the phase sensitivity of said second position indicating signal, said first receiver being operative when said third receiver is receiving said fourth pair of waves to receive and reproduce first and second reference signals modulated on a common carrier and respectively having frequencies equaling the frequencies of said second and fourth position indicating signals, said second receiver b i p tive wh n said third receiver is reaeaaseo ceiving saidithird pair of waves to receive and reproduce third and fourth reference signals modulated on a common carrier and respectively having frequencies equaling the frequencies of said first and third position indicating signals, whereby four pairs of matching frequencyrefer ence and position indicating signals are alternately produced in sets of two; thetwo pairso'f signals constituting each set having different phase sensitivities, a plurality of pliase'measur in'g m'eans'for respectively measuring the phase relationship between said matching frequency pairs, normally closed gate means coupled'to th'e in'pu't circuits of each of said phase measuring means for normally isolating said p'haseiin'easur ing means, said gate meansbeing respectively is sponsive to said reference signals for supplying said matching signals to said phase measuring means for phase comparison.

20. A wave signal receivingapparatus for translating received space radiated waves into position indications, comprising a first receiver for receiving a first pair of space" radia'tedwaves and for heterodyning said waves to produce a first position indicating signal having a frequency related to the difference frequency between said pair of Waves, a second receiver for receiving and heterodyning a second pair of radiated waves to produce a second positionindicating signalihav-i ing a frequency related to the diiference frequency between said second pair of waves, a third receiver alternately operative to receive and heterodyne third and fourth pairs of waves to produce heterodyne' signals having frequencies respectively related to the difference freq encies of said thirdand fourth pairs, heterodyne means responsive to said first position indicating's gnal and said third'heterodyne' signal for produc": ing a third position indicating signal'havih phase sensitivity different than the'phases Y tivity of said first position indicating signal; other heterodyne means responsive to'said secend position indicating signal and said fourth heterodyne signal for producing a feur'tnpo si: tion indicating signal having a phase sensitivity different than the phase sensitivity of sensesnd position indicating signal, said first receiver being operative when said third reee'ivei is re ceiving said fourth pair of waves tc rceivand reproduce first and second reference si als modulated on' aeommon carrier andrsfictively having frequencies equaling the frequencies of said second andfourth position indicating sig' nals, said second receiver being operative w en said third receiver is receiving" said thirdieair cf waves to receive and reproduce third and sauna reference signals modulated on a common carrier and respectively having frequencies ediialin'g the frequencies of said first and third assists indicating signals, whereby four pairs of diet hing frequency reference and position indicating signals are alternately produced in sets of two, the two pairs of signals eqiistitunng each having different phase sensitivities, said one and fourth reference signals Being in the forfii of short pulses having a duration whichhears the same relation to the time between poise as the ratio between the phase sensitivities of said matching frequency pairs, a plurality of ph 'ss'; measuring means for respectively measuring *th 7 phase relationship between said matching frequency pairs, normally closed gatemeans coupled to the input circuits of each of said phase 'rheas uring means for normally isolating said phase measuring means, said gate means being re spectively responsive tosaidreferen'ce signalsfor supplying said m'atc'htmg signals to said phase" measuring means'for phase comparison;

21; A wave' signal receiving apparatus for for receiving a first pair of space radiated waves" and for heterodyning said 'waves' to produce a first position indicating signal having" a frequency related tdthe'difierence frequency between said pair of waves, a second receiver for receiving and'h'eterodyning a second pair'of radiated waves to producea'se'cond position indicating signal having a frequency related 'to'thediffe're'nce freiiii'ency oetween said second pair" of waves; aj'th'ird receiver al terriately'opera'tiv'e to receive and heterouyne th" d 'and fourth pairs of waves to produce-'heterodyne signals having'frequencies respectively related to the"difference' frequencies of said third and' fourth pairs, h'eterodyne means res onsive to" said first posi-' tion indicating signal said third heterodyne signal for p'rodu "ing athird'position indicating signer otnefheterodyne means responsive tosaid second position indicating signal-arid said fourth h terodynesignai for'prouucing' a fourth position indicating signer said first receiver heihgofierati ve when said third-r cei er isreceiving'said foiirth'pair of waves 0 receive andreproduce first and seccrid' erere ice ignals modulated on a common carrier and respectively having ire-'- duencie's equaling-the frequencies of said second and fourth position indicating signals, said'secol'id receiver being operative when said third re- Civ'r isfeofififig salid fl'iira pair" of Waves to re cave and reproduce tnird and fourth reference" signals modulated ona common carrier'and respe'etiveiy having frequeiicies' e ualing the freiie'ncies of said; first and third position indicating' signals, where y; four pairs of matching frequency reference and position indicating signals are alternately produced in sets or two, a pair'of phase measuring meansror respectively-measuringthe phasereiation nip between said first position i-iidicat I signal and said third reference and between s'aiii thirdiposition indicating s1 signal, and said r 'rth r'e'feiencesignal to produes' two indications" or the position or said rei /iii'g apparatus relative to the source of one of 5'21 01 waves, a 00nd pair of phase measuring iiiea'ns'for respectively measuring the phase relatio'rishifi between said second osition indicatiiig signal. and Said first ffrehcesignal and between s'aid foii'itlipositiori indicating Signal and Said Second'iferei'icefsigiialto produce two indications of the position of said receiving apparatus relative to the source of another of said waves, normally closed gate means coupled to the iii iit circuits of each of said phase measuring means for normally isolating said phase measurin means, said gate means being respectively res'poiisive to said reference signals for supplying sa d' matching signals to said phase measuring means' or phasecornparisoii;

22. A wave signal receiving apparatus for translating received sp I position; indications, comprising a first receiver for receiving a firstpair of space radiated waves and for heterodyning said waves to produce a first positionindicating signal havinga frequency diated waves into' 

